10amp drain thru rear defroster, with the key off

[LaxCoachT]

Last week, went to start my 09 tahoe (180K miles) and battery was completely dead.
Battery was at least 8 years old, figured it was time to replace.

Put a new one in and it was dead overnight.
Diconnected and charged it.
Reconnect and check draw, 10amps with no key in the ignition.

Start checking fuses and the 30A one for rear defroster is hot to the touch.
Check the defroster relay, it's functioning normally.
Bought a new relay just in case, still drawing 10A after swapping it in.

I pulled one of the leads on the rear window defroster and the draw stops immediately.
If I check between the lead and the defroster tab, I get the 10A

The on/off botton on the climate controls is not hot, so I don't think it's seeing the current.

Could there be a short in the fuse box itself?
If I pop it out, would i be able to see anything on the back side?

Any thoughts on where else to look?

Thanks



Thanks

 

[pa31p]

Does the draw stop when you pull relay out ?

bad grounding can cause weird things, start checking for that as well, specially braided type ground wires.

 

[LaxCoachT]

Does the draw stop when you pull relay out ?

bad grounding can cause weird things, start checking for that as well, specially braided type ground wires.

Removing relay does not stop the draw. Should've mentioned that.
Once my coffee finishes brewing, I will go dig into the grounds and pull the fusebox.
Can't think without caffine...

 

[Doubeleive]

I would ohm test each end of the defrost wires one of them might be shorted somewhere. maybe there is a pinched wire in the harness and unless it is something easily spotted might be hard to find.
I could be completely wrong but it is something I would check first just to see if it is that simple

 

[LaxCoachT]

Wire on defroster checked out OK. Grounds also checked OK.

I popped the fuse box out.
The pins on the back side are not marked.
Is there a diagram of the back side so I can check the pins to see if anything is shorted out?

 

[exp500]

Since you know it's defrost fuse, count spaces/rows and flip over.

 

[pa31p]

Another thought, open/close the hatch, see if draw changes while moving. maybe there’s a short in the wire bundle in the back end

 

[LaxCoachT]

EXP500: got too cold yesterday, I had to put it all back together so I could get to work today. Will pop it out again this weekend and start counting. Gives me something to do on Blk Friday.

pa31p: I looked at the loom and didn't see anything when it first happened. I'll pull the boot back, maybe pop the trim inside if it's not a big PITA.

Scratching my head how it's getting that much current with the key off and a functional rear defrost relay.

 

[Fless]

EXP500: got too cold yesterday, I had to put it all back together so I could get to work today. Will pop it out again this weekend and start counting. Gives me something to do on Blk Friday.

pa31p: I looked at the loom and didn't see anything when it first happened. I'll pull the boot back, maybe pop the trim inside if it's not a big PITA.

Scratching my head how it's getting that much current with the key off and a functional rear defrost relay.

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[Doubeleive]

Wire on defroster checked out OK. Grounds also checked OK.

I popped the fuse box out.
The pins on the back side are not marked.
Is there a diagram of the back side so I can check the pins to see if anything is shorted out?

I think you may have misunderstood what I meant. the glass wire grid would not have anything to do with it, unless the grid was broken and the defrost did not function at all.
the wires that connect to the grid are what would need to be checked
disconnect both grid wires, put your meter on ohm's then a probe on one of the wires that connects to the grid and the other probe end to a good body ground point
record or memorize the ohm reading, then check the other grid wire same manner. I'm thinking one of the wires may be a open circuit until the defrost is activated which would make sense so if both are grounded then maybe that might help determine the source of the problem.
just guessing.....